1. Technical Field
The present invention relates to a chemical mechanical polishing apparatus, and more particularly, to a chemical mechanical polishing apparatus to prevent scratches caused by a direct friction between a polishing pad and a wafer.
2. Discussion of the Related Art
Recently, the number of devices integrated into one fingernail-sized semiconductor chip has approached, and in some cases exceeded, 1×109. Furthermore, the number of devices integrated into one semiconductor chip is increasing by geometrical progression. To obtain both high integration and a high speed in such devices, it is necessary to improve the development of the semiconductor chip in both structural and material aspects. The improvement in the structure of the semiconductor chip involves the increase in the number of metal layers. Also, a shallow trench isolation (STI) method is used for isolation between the devices. In such devices, the semiconductor chip is formed of materials including copper (Cu) and low-dielectric material (Low-k).
A CMP (Chemical Mechanical Polishing) process becomes increasingly important as the number of metal layers increases. Generally, a semiconductor device is formed by selectively and repeatedly performing processes of photo etching, diffusion, and metal deposition on a wafer. For formation of the semiconductor device, it is necessary to repeatedly perform the CMP process for planarization and etch-back on the wafer, that is, to obtain the easiness when forming predetermined circuit patterns on the surface of the wafer.
When performing the CMP process, in a state that the surface of the wafer is in contact with a surface of a polishing pad, a slurry in which abrasives are scattered is provided thereto, thereby generating a chemical reaction. In addition, a carrier which holds a polishing table and the wafer is relatively moved, whereby the desired layer is polished mechanically, thereby planarizing the entire surface of the semiconductor device.
Hereinafter, a chemical mechanical polishing apparatus according to the related art will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view of showing a chemical mechanical polishing apparatus according to the related art. As shown in FIG. 1, a chemical mechanical polishing apparatus according to the related art is provided with a polishing table 21, a polishing head 30, a slurry supplier 50, and a pad conditioner 40.
At this time, a polishing pad 20 is adhered to an upper side of the polishing table 21. The polishing head 30 is mounted on a wafer 10 including an insulating layer or a metal layer. Then, the slurry supplier 50 is provided to supply slurry to the surface of the polishing pad 20. Also, the pad conditioner 40 grinds the polishing pad 20 in the different parts from a wafer rotation part during the polishing process.
That is, after the wafer 10 is closely adhered to the polishing table 21, the wafer 10 is rotated, and the polishing table 21 is rotated, at the same time. Thus, it is possible to perform the mechanical polishing between the wafer and the polishing pad. Then, the slurry is supplied between the wafer 10 and the polishing pad 20 through the slurry supplier 50. As a result, the slurry reacts with the insulating or metal layer of the wafer, thereby performing the chemical polishing.
For improvement of the preciseness in planarization of the device by the CMP process, it is necessary to maintain the appropriate roughness in the surface of the polishing pad 20 being in contact with the wafer, and the entire elasticity. For this, the pad conditioner 40 controls the surface state of the polishing pad 20.
In more detail, the polishing head 30 is provided with a manifold 34, a carrier 33, a retainer ring 31, and a porous plate (not shown). At this time, air supplied from the exterior through an air hole of the manifold 34 is dispersed inside the polishing head 30. The carrier 33 corresponds to a body of the polishing head 30, wherein the carrier 33 serves as the center for connection with other parts. Also, the retainer ring 31 prevents the separation of the wafer during the process. The porous plate (not shown) includes a plurality of holes, through which the air supplied from the air holes of the manifold is applied to a membrane 32 with pressure. The membrane 32 is an elastic body for covering a portion to which the wafer is fixed. As the air is supplied through the holes of the porous plate, the wafer is pressed by the air. Thus, during the chemical mechanical polishing process, the wafer is in contact with the polishing pad under the uniform pressure.
In the chemical mechanical polishing apparatus, when the polishing table 21, on which the polishing pad 20 is adhered, is rotated at a high speed, the slurry supplier 50 uniformly provides the slurry to the surface of the polishing pad. In this state, when the wafer 10 is oscillated from one side of the polishing table 21 to the other side of the polishing table 21 by the polishing head, and is also rotated at a high speed. Accordingly, the surface of the wafer is planarized with both the chemical reaction using the slurry and the mechanical reaction using the high speed rotation. After that, the slurry, which reacts with the wafer, is discharged to the outside of the polishing pad.
In the meantime, the surface roughness of the polishing pad is changed according to the mechanical friction between the polishing pad and the wafer. Therefore, a conditioning process for grinding the surface of the polishing pad with the polishing conditioner 40 is performed at fixed periods.
During the conditioning process, the polishing pad 20, adhered on the polishing table 20, is rotated at a high speed, and the polishing conditioner 40 having a grinding means such as diamond is positioned adjacent to the polishing table 20. In this state, the polishing conditioner 40 is oscillated and is rotated at a high speed.
The polishing pad is formed of a high molecular material, for example, polyurethane. With the relative movement of the wafer and the supply of slurry, it is possible to polish the surface of wafer.
Accordingly, the characteristics of slurry and polishing pad have great effects on the CMP process. Especially, the polishing pad is in direct contact with the wafer, so the surface state of the CMP polishing pad has great effects on polishing ratio, uniformity and defective ratio.
In the meantime, the CMP process is performed to planarize an over-filled insulating layer or metal layer. For example, when forming a plug for connection between a lower line layer and an upper line layer, the metal layer is gap-filled inside a contact hole on the lower line layer exposed throughout the contact hole, and then the over-filled metal layer is removed, thereby realizing the planarization in surface of the wafer.
However, the chemical mechanical polishing apparatus according to the related art has the following disadvantages.
The CMP process is useful for the planarization of device. However, in a state that the polishing pad is in direct contact with the wafer, the mechanical polishing is performed with oscillating movement and high-speed rotation. Thus, many scratches may be formed on the surface of the wafer.
Especially, in a high-integration semiconductor device, an RC delay of lines, which are related with the minuteness of semiconductor device, is relatively larger than RC delay of transistor devices. Also, as the line resistance increases, the lines are desirably formed of copper which has great conductivity and low resistance. However, copper is softer than aluminum, which may be scratched more readily during a CMP process.